Which rotator cuff muscle initiates the first few degrees of arm abduction?

The supraspinatus muscle is responsible for initiating the first few degrees of arm abduction, making it essential for this movement pattern. The supraspinatus is one of the four rotator cuff muscles, and its primary function is to stabilize the shoulder joint while also assisting with arm elevation. The muscle's fibers run from the supraspinous fossa of the scapula to the greater tubercle of the humerus.

When the arm begins to move away from the body, the supraspinatus activates to lift the humeral head and allow for smooth movement in the shoulder joint. It plays a crucial role in the initial phase of abduction, as other muscles may become more active as the movement progresses beyond those first degrees of motion.

The other rotator cuff muscles, such as the infraspinatus, teres minor, and subscapularis, serve different functions—such as external rotation and internal rotation of the arm—but do not initiate abduction in the way the supraspinatus does. Therefore, identifying the supraspinatus as the muscle that initiates arm abduction lays a solid foundation for understanding shoulder mechanics and the choreography of movement in this joint.